An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, wherein in a full-charge high-temperature 130 DEG C state, a diisocyanate functional group in the electrolyte reaches a temperature required for a polymerization reaction at high temperature, a pyridine compound containing a diisocyanate functional group and a vinyl functional group is subjected to a polymerization reaction, a six-membered ring structure with three active isocyanate groups, i.e. isocyanuric acid, is generated, and an unsaturated double bond (vinyl) further increases the polymerization degree of the polymer at high temperature, a generated polymer forms a blocking layer on an electrode surface, so that the internal resistance of the battery rapidly increases, thereby slowing down or preventing further decomposition of the electrolyte, gas and heat generated can be significantly reduced, and then thermal runaway of the battery is prevented, so that the battery is in a safe state.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolyte and a battery comprising the same, and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] Lithium ion batteries have the advantages of high specific energy density and long cycle life, and are widely used in various electronic products. In recent years, they have also been widely used in electric vehicles, various electric tools and energy storage devices. With the improvement of people's living standards and the pursuit of a better life, higher requirements have been put forward for the energy density of batteries.

[0003] With the increasing use of lithium ion batteries in various fields, the size of the batteries is also increasing, and the safety performance of the batteries becomes particularly important. The safety performance of the current lithium ion battery mainly depends on the control of the voltage and temperature range. Within a certain safety boundary, the battery can be very safe, but if the safety boundary is exceeded, the battery becomes very dangerous. The high temperature test can be carried out by using a heat chamber test. The heat chamber test simulates the situation of the battery being used improperly at high temperature, such as placing a mobile phone in a sun-exposed car, or placing a mobile phone or electronic product in a microwave oven, the temperature can reach 130℃ or even 150℃. When the battery is in a thermal abuse state, the heat source comes not only from the reaction between the positive and negative materials inside the battery and the electrolyte, but also from the shrinkage of the separator film at high temperature, which leads to short circuit between the positive and negative electrodes. The joule heat generated by the short circuit is also an important heat source in the heat chamber test. SUMMARY

[0004] In order to solve the safety problems of lithium ion batteries under high temperature and high voltage, the present application provides an electrolyte and a battery comprising the same. The electrolyte can improve the safety performance of the battery under high temperature and high voltage. The preparation process of the electrolyte is simple, the cost is low, and the protection effect is good.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] An electrolyte, comprising an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive selected from a pyridine compound containing a diisocyanate functional group and a vinyl functional group.

[0007] According to an embodiment of the present application, the pyridine compound containing a diisocyanate functional group and a vinyl functional group comprises a pyridine ring, a vinyl group and two isocyanates, and the two isocyanates (O=C=N-) are connected to the pyridine ring through R1 and R2 respectively, and the vinyl group is connected to the pyridine ring through R3, R1, R2 and R3 are the same or different and are independently selected from the group consisting of nothing, C 1～10 alkylene.

[0008] According to an embodiment of the present invention, the pyridine compound containing a diisocyanate functional group and a vinyl functional group has a structural formula shown in Formula I:

[0009]

[0010] In formula I, R1, R2, and R3 are the same or different and are independently selected from the group consisting of: 1～10 Alkylene.

[0011] According to an embodiment of the present invention, R1, R2, R3 are the same or different and are independently selected from the group consisting of: 1～6 Alkylene.

[0012] According to an embodiment of the present invention, R1, R2, R3 are the same or different and are independently selected from the group consisting of: 1～3 Alkylene.

[0013] According to an embodiment of the present invention, R1, R2, R3 are the same or different and are independently selected from the group consisting of absence, methylene, ethylene or propylene.

[0014] According to an embodiment of the present invention, the first additive can be prepared by a method known in the art, or can be purchased through commercial channels.

[0015] According to an embodiment of the present invention, the pyridine compound containing a diisocyanate functional group and a vinyl functional group is selected from at least one of the compounds represented by the following formulas 1 to 8:

[0016]

[0017] According to an embodiment of the present invention, the weight of the first additive is 0.1wt% to 5.0wt% of the total weight of the electrolyte, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.3wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt% or 5wt%.

[0018] According to an embodiment of the present application, the electrolyte salt is selected from electrolyte lithium salts selected from one or more than one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalato borate (LiDFOB), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide or lithium bis(trifluoromethylsulfonyl)imide.

[0019] According to an embodiment of the present application, the electrolyte salt is present in a weight amount of 11 wt% to 18 wt% of the total weight of the electrolyte, for example 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt% or 18 wt%.

[0020] According to an embodiment of the present application, the organic solvent is selected from carbonates and / or carboxylic esters, the carbonates being selected from one or several of the following solvents, fluorinated or not: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate; the carboxylic esters being selected from one or several of the following solvents, fluorinated or not: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, ethyl n-butyrate.

[0021] According to an embodiment of the present application, the functional additive further comprises a second additive selected from nitrile compounds selected from at least one of adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN), butanedinitrile, glycerol trinitrile.

[0022] According to an embodiment of the present application, the second additive is present in a weight amount of 2 wt% to 8 wt% of the total weight of the electrolyte, for example 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt% or 8 wt%.

[0023] According to an embodiment of the present application, the functional additive further comprises a third additive selected from at least one of fluorinated ethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3-propene sultone, lithium difluoro oxalato borate, lithium difluorophosphate, lithium difluorobisoxalate phosphate.

[0024] According to an embodiment of the present application, the third additive has a weight of 8wt% to 15wt% of the total weight of the electrolyte, for example 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0025] According to an embodiment of the present application, the electrolyte is used in a battery, preferably in a lithium ion battery.

[0026] The present application also provides a battery comprising the electrolyte described above.

[0027] According to an embodiment of the present application, the battery further comprises a positive electrode sheet comprising a positive electrode active material, a negative electrode sheet comprising a negative electrode active material, and a separator.

[0028] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive agent and a binder.

[0029] According to an embodiment of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent and a binder.

[0030] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is 80wt% to 99.8wt% of the positive electrode active material, 0.1wt% to 10wt% of the conductive agent, and 0.1wt% to 10wt% of the binder.

[0031] Preferably, the mass percentage of each component in the positive electrode active material layer is 90wt% to 99.6wt% of the positive electrode active material, 0.2wt% to 5wt% of the conductive agent, and 0.2wt% to 5wt% of the binder.

[0032] According to an embodiment of the present application, the mass percentage of each component in the negative electrode active material layer is 80wt% to 99.8wt% of the negative electrode active material, 0.1wt% to 10wt% of the conductive agent, and 0.1wt% to 10wt% of the binder.

[0033] Preferably, the mass percentage of each component in the negative electrode active material layer is 90wt% to 99.6wt% of the negative electrode active material, 0.2wt% to 5wt% of the conductive agent, and 0.2wt% to 5wt% of the binder.

[0034] According to an embodiment of the present application, the conductive agent is selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

[0035] According to an embodiment of the present application, the binder is selected from at least one of sodium carboxymethylcellulose, styrene butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0036] According to an embodiment of the present application, the negative active material comprises a carbon-based negative material and / or a silicon-based negative material.

[0037] According to an embodiment of the present application, the silicon-based negative material is selected from at least one of nano-silicon, silicon-oxygen negative material (SiO x (0 < x < 2) or silicon-carbon negative material.

[0038] According to an embodiment of the present application, the carbon-based negative material is selected from at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0039] According to an embodiment of the present application, the mass ratio of the silicon-based negative material to the carbon-based negative material in the negative active material is 9:1-1:9, for example, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, or 9:1.

[0040] According to an embodiment of the present application, the positive active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, and lithium manganate; the transition metal lithium oxide has a chemical formula of Li 1+x Ni y Co z M 1-y-z O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.

[0041] According to an embodiment of the present application, the charge cut-off voltage of the battery is greater than or equal to 4.5 V.

[0042] The present application has the following beneficial effects:

[0043] The electrolyte and the battery including the electrolyte are provided, in which the diisocyanate functional group in the electrolyte reaches the temperature required for polymerization reaction at high temperature, the pyridine compound containing the diisocyanate functional group and the vinyl functional group is polymerized to generate a six-membered ring structure with three active isocyanate groups, i.e., isocyanuric acid, and the unsaturated double bond (vinyl) further increases the polymerization degree of the polymer at high temperature, so that the generated polymer forms a blocking layer on the electrode surface, the internal resistance of the battery is rapidly increased, and thus the further decomposition of the electrolyte is slowed down or prevented, the generated gas and heat are significantly reduced, and the thermal runaway of the battery is prevented, so that the battery is in a safe state. In addition, the pyridine compound containing the diisocyanate functional group and the vinyl functional group can also be used in combination with the nitrile compound, and the pyridine compound containing the diisocyanate functional group and the vinyl functional group can preferentially combine with the proton H + Thus, the proton H + The combination of the pyridine compound containing the diisocyanate functional group and the vinyl functional group and the nitrile compound in the present application can also better stabilize the positive electrode / electrolyte interface properties compared to the single nitrile compound. DETAILED DESCRIPTION

[0044] The present application will be further described in conjunction with specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology achieved based on the above description of the present application is included in the scope of protection intended by the present application.

[0045] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0046] To make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0047] It can be understood that the lithium ion battery of the present application includes a negative electrode sheet, an electrolyte, a positive electrode sheet, a separator and an outer package. The positive electrode sheet, the separator and the negative electrode sheet are stacked to obtain an electrode core, or the positive electrode sheet, the separator and the negative electrode sheet are stacked and then wound to obtain an electrode core, and the electrode core is placed in the outer package, and the electrolyte is injected into the outer package to obtain the lithium ion battery of the present application.

[0048] The lithium ion battery of Example 1-12 and Comparative Example 1 was prepared by the following steps:

[0049] 1) Preparation of positive electrode sheet

[0050] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotube (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was performed under the action of a vacuum stirrer until the mixed system became a positive active paste with uniform fluidity; the positive active paste was uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil was dried, then rolled, and cut to obtain the desired positive electrode sheet.

[0051] 2) Preparation of negative electrode sheet

[0052] Artificial graphite, silicon monoxide, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotube (SWCNTs) were mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, deionized water was added, and a negative active paste was obtained under the action of a vacuum stirrer; the negative active paste was uniformly coated on both surfaces of a copper foil; the coated copper foil was air-dried at room temperature, then transferred to a 80°C oven for drying for 10h, then cold-pressed and cut to obtain the negative electrode sheet.

[0053] 3) Preparation of electrolyte

[0054] In an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm), EC / PC / DEC / PP were mixed in a mass ratio of 1:1:2:6, then 1mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added, after dissolution, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN) and the first additive (the specific electrolyte formula is shown in Table 1) were added, and the electrolyte was injected into the dried battery, respectively.

[0055] 4) Preparation of lithium ion battery

[0056] The positive electrode sheet of step 1), the negative electrode sheet of step 2) and the separator were stacked in the order of positive electrode sheet, separator and negative electrode sheet, then wound to obtain a battery core; the battery core was placed in an outer packaging aluminum foil, the electrolyte of step 3) was injected into the outer packaging, and the lithium ion battery was obtained after vacuum packaging, standing, formation, shaping, sorting and other processes. The battery of the present application has a charge-discharge range of 3.0-4.5V.

[0057] Table 1 Composition of electrolyte of examples and comparative examples

[0058] LiPF6 FEC First additive and content ADN HTCN PS Example 1 13 wt% 8 wt% Formula 1 / 2 wt% 2 wt% 2 wt% 4 wt% Example 2 13 wt% 8 wt% Formula 2 / 2 wt% 2 wt% 2 wt% 4 wt% Example 3 13 wt% 8 wt% Formula 3 / 2 wt% 2 wt% 2 wt% 4 wt% Example 4 13 wt% 8 wt% Formula 4 / 2 wt% 2 wt% 2 wt% 4 wt% Example 5 13 wt% 8 wt% Formula 5 / 2 wt% 2 wt% 2 wt% 4 wt% Example 6 13 wt% 8 wt% Formula 6 / 2 wt% 2 wt% 2 wt% 4 wt% Example 7 13 wt% 8 wt% Formula 7 / 2 wt% 2 wt% 2 wt% 4 wt% Example 8 13 wt% 8 wt% Formula 8 / 2 wt% 2 wt% 2 wt% 4 wt% Comparative Example 1 13 wt% 8 wt% / 2 wt% 2 wt% 4 wt% Example 9 13 wt% 8 wt% Formula 1 / 1.5 wt% 2 wt% 2 wt% 4 wt% Example 10 13 wt% 8 wt% Formula 1 / 1 wt% 2 wt% 2 wt% 4 wt% Example 11 13 wt% 8 wt% Formula 1 / 0.5 wt% 2 wt% 2 wt% 4 wt% Example 12 13 wt% 8 wt% Formula 1 / 2 wt% / / 4 wt%

[0059] The lithium ion batteries obtained from the examples and comparative examples were subjected to 45℃ cycle performance test and 130℃ safety performance test, respectively, and the test results are shown in Table 2.

[0060] 1) 45℃ cycle performance test

[0061] The batteries in Table 1 were subjected to charge-discharge cycling at 45℃ within the charge-discharge cut-off voltage range at a rate of 1C for 1000 cycles, the discharge capacity of the first week was counted as x1 mAh, and the discharge capacity of the Nth cycle was counted as y1 mAh; the capacity of the Nth week divided by the capacity of the first week gave the cycle capacity retention rate R1 of the Nth week = y1 / x1.

[0062] 2) Safety performance test

[0063] First, the battery after formation and partial discharge was allowed to stand for 10 min, then discharged at 0.2C to 3V, allowed to stand for 10 min, then charged at 0.5C to full capacity, cut off at 0.05C, and allowed to stand for 10 min. The full charge state voltage, internal resistance, and thickness of the battery were tested at 25±5℃, the battery was placed in a 130℃ thermal shock test chamber, and the temperature was increased to 135℃ at a rate of 6℃±2℃ / min and maintained for 30 min to monitor the voltage and bulk temperature rise.

[0064] Table 2 Performance test results of the batteries of the examples and comparative examples

[0065]

[0066] From the comparison between Comparative Example 1 and Examples 1-8 in Table 2, it can be seen that the pyridine compound containing diisocyanate functional groups and vinyl functional groups significantly improves high-temperature cycling, and more importantly, after adding an appropriate amount (2wt%) of the pyridine compound containing diisocyanate functional groups and vinyl functional groups, the 130℃ safety performance test does not catch fire or explode, while the comparative group without addition catches fire and explodes, indicating that the pyridine compound containing diisocyanate functional groups and vinyl functional groups has undergone a polymerization reaction at high temperature (130℃), and the polymer forms a blocking layer on the surface of the electrode, causing the internal resistance of the battery to rapidly increase, thereby slowing down or preventing further decomposition of the electrolyte, significantly reducing the generated gas and heat, and thus preventing thermal runaway of the battery, keeping the battery in a safe state.

[0067] As can be seen from Table 2, Examples 1, 9-11 and Comparative Example 1, different amounts of the pyridine compound containing diisocyanate functional groups and vinyl functional groups have different effects on the high-temperature cycle performance, wherein the performance of 1 wt% of the pyridine compound containing diisocyanate functional groups and vinyl functional groups shown in Formula 1 is optimal, and at the same time, can meet the requirements of no fire and no explosion, and the battery of Example 11 can be due to the insufficient amount of the pyridine compound containing diisocyanate functional groups and vinyl functional groups, resulting in insufficient polymerization degree, and the fire phenomenon occurs in the safety test, and the cycle performance is relatively weak.

[0068] As can be seen from Table 2, Examples 1, 12 and Comparative Example 1, the pyridine compound containing diisocyanate functional groups and vinyl functional groups can also be used in combination with nitrile compounds, and the pyridine compound containing diisocyanate functional groups and vinyl functional groups can preferentially combine with the protons H + , thereby avoiding the protons H + from weakening the complexing ability of the nitrile compound, and compared with the single nitrile compound, the combination of the pyridine compound containing diisocyanate functional groups and vinyl functional groups and the nitrile compound of the present application can also better stabilize the properties of the positive electrode / electrolyte interface.

[0069] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive selected from a pyridine compound containing a diisocyanate functional group and a vinyl functional group; The pyridine compound containing a diisocyanate functional group and a vinyl functional group has a structural formula shown in Formula I: In formula I, R1, R2, and R3 are the same or different and are independently selected from the group consisting of: 1～10 alkylene; The weight of the first additive is 0.1 wt% to 5.0 wt% of the total weight of the electrolyte.

2. The electrolyte according to claim 1, characterized in that The functional additive further includes a second additive, which is selected from nitrile compounds, and the nitrile compound is selected from at least one of adiponectin (ADN), 1,3,6-hexanetrionitrile (HTCN), succinonitrile, and glycerol trinitrile.

3. The electrolyte according to claim 2, characterized in that The weight of the second additive is 2 wt% to 8 wt% of the total weight of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The functional additive further includes a third additive, which is selected from at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3-propylene sultone, lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorobis(oxalatophosphate).

5. The electrolyte according to claim 4, characterized in that The weight of the third additive is 8 wt % to 15 wt % of the total weight of the electrolyte.

6. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 5.

7. The battery according to claim 6, characterized in that The charging cut-off voltage of the battery is greater than or equal to 4.5V.

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